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Spindle Lock Repair for HF 4.5" Grinders

07-20-2014, 11:50 AM

I own a really nice variable speed Milwaukee 4-1/2" grinder and I love it. I use it for all of my heavy duty 4-1/2" grinding work.

I have two Harbor Freight grinders and they have worked ok except for the spindle lock. I like to use the Harbor freight grinders for the lighter work such as the cut off disk, the wire brush or the flap wheel. I find it easier to grab a different grinder instead of changing the wheel. You might wonder why I didn't throw them out instead of fixing them:

First of all I took it as a challenge to fix them.

I also hate to throw something out that still had a lot of life left.

Last but not least, like most people that I know with mechanical ability, I can be stubborn.

Back to my repair project:

1. On the first grinder the tip of the locking pin broke off, but it was no big deal I turned a replacement pin on my lathe from a M6 socket head cap screw. The old and new pins can be seen on picture 1. My repair has worked fine ever since.

2. On the second grinder the spindle lock failed by fracturing the casting as shown in picture 2.

3. Once the spindle lock failed it allowed the pin to rotate which put excessive force on the plastic head of the pin which caused it to shatter.

A pin with the plastic head in place is in the bottom of picture 3

The pin that had the shattered head is in the middle

The top of the picture shows the M6 socket head cap screw that I turned to make a replacement pin

4. As much as I like welding, I was afraid that the die cast gearbox might be an alloy that contained zinc, which would make it unweldable. Instead of welding I made an aluminum bushing to replace the damaged casting. An exploded view of the pin assembly with the new bushing is shown in picture 4.

6. Picture 6 shows a drawing of the cross section of the bushing, casting and locking pin. In addition to the thread, I also used Loctite 680 on the entire OD of the bushing to retain it in the casting.

7. Picture 7 shows the setup on my milling machine to bore out the casting to accept the bushing.

I think I will pick up a few.
I like to mount different type grinding wheels on different grinders and change grinders as opposed to changing wheels, because it is quicker.
Thanks for the tip and the endorsement.

I will most likely still use my 11 amp variable speed Milwaukee for the heavy grinding.

Comment

First of all I took it as a challenge to fix them.
I also hate to throw something out that still had a lot of life left. Last but not least, like most people that I know with mechanical ability, I can be stubborn.

My kind of guy; you and I could surely swap stories for hours!

I started buying HF 4 1/2" side grinders some years back when the American brand I had used for years off-shored their manufacturing to China and their quality went down. The local rep for that company heatedly denied that there was any difference, and that they had inspectors in China and that their quality was as good as ever. Well it d@mned-well was not!! When the "American" made-in-China grinder costs $95 and lasts only seven-eight months, and the openly-Chinese HF grinder costs $20 and lasts three months, I'm willing to buy HF, even though all HF stuff sounds like the bearings are bad right out of the box. Like you, I also have good grinders, and just use the HF ones for skut-work. The one good aspect, for guys like you and me, is that pretty soon you have a box with two or three dead HF grinders for parts. Well, the other good aspect is that if the HF stuff get stolen, you haven't lost much, and the thief hasn't gained much.

If anybody else here is willing to lower his standards far enough to buy HF 4" or 4 1/2" sidegrinders, get the $20-25 version with the yellow or wine-colored housing. There is a cheaper grinder with a black housing (called "Workmaster," I think), and when they were on sale for ten bucks each I bought three of them, but the best one only lasted a couple of weeks, and one smoked its motor in the first half-hour. It's not always true that you get what you pay for (see that faux-American $95 grinder), but this time $30 for three sidegrinders was a lousy deal.